Guiding and feeding device for a work bar in a lathe

ABSTRACT

A hollow spindle (10) comprises a collet (20) at one end and behind the same and spaced from each other two guide sleeves (50,52) for the work bar (W). The rear guide sleeve (52) being the most remote from the collet (20) is axially displaceable in a direction toward the collet (20) against the resistance of a spring (58) and has an abutment face (82) remote from the collet (20) for a stock feeder (70). Upon advanced use of the work bar (W) the stock feeder (70) hits the abutment face (82) of the rear guide sleeve (52), pushing the same forwardly as the work bar (W) continues to be used up and advanced. By virtue of this arrangement the work bar (W) is guided in vibrationless manner and also the stock feeder (70) is kept largely without vibrating by its abutment against the rear guide sleeve (52).

The invention relates to a guiding and feeding device for a work bar ina lathe, comprising a hollow spindle which includes a chuck at one endand behind the same and spaced from each other at least two guidesleeves for the work bar, and a stock feeder for advancing the work barin a direction toward the chuck.

With known guiding devices of this kind (journal "tz furMetallbearbeitung" no. 5/83 and no. 6/83) there are three guide sleevesstationarily arranged within the spindle, the first one directly behindthe chuck and the other two at uniform spacings behind the same. Theguide sleeves have an inner diameter closely adapted to the outerdiameter of the work bar to be processed. A bar material magazine isarranged behind the spindle and comprises a plurality of roller setsbetween which the work bar is rotatably supported. A telescopic stockfeeder is coordinated with the bar material magazine and disposedcoaxially with the work bar behind the latter. It comprises an axiallydisplaceable tubular outer feeder as well as a rod-like inner feederguided for axial displacement in the outer feeder. The diameter of theinner feeder is smaller than the diameter of the work bar.

When a new work bar is introduced from behind into the spindle and itsguide sleeves as well as the chuck, with this known arrangement, therear end of the work bar is supported and held centered at the front endof the outer feeder. During operation of the lathe the work bar is fedstep by step by the stock feeder, the outer and inner feeders moving incommon until the front end of the outer feeder has reached a position ata small distance behind the rearmost guide sleeve of the spindle.Further forward movement of the outer feeder is impossible since itsouter diameter is larger than the inner diameter of the guide sleeves.The further advance of the work bar is taken care of by the inner feederwhich now is being pushed forward with respect to the outer feeder,penetrating the guide sleeves one after the other and finally the chuckuntil the work bar has been used up and any possible remainder has beenejected by the inner feeder in forward direction through the chuck.

The guide sleeves are exchangeable so that in each case guide sleevescan be used whose inner diameter is closely adapted to the diameter ofthe work bar. Yet the stock feeder, particularly the inner feeder isused unchanged for work bars of different diameters because it would betoo expensive to restructure the stock feeder for each change of stockdiameter. For this reason normally the outer diameter of the innerfeeder cannot be adapted closely to the inner diameter of the guidesleeves in the spindle. Consequently there is more or less great radialclearance for the inner feeder in the guide sleeves. The same applies inthe event that the stock feeder is not of telescopic design but insteadincludes a single rod only of slender configuration to be slipped intothe guide sleeves.

In both cases guide sleeves adapted to the diameter of the bar materialcannot guide the stock feeder at the same small radial clearance as thework bar. Thus the front portion of the stock feeder which has enteredthe guide sleeves tends to become somewhat eccentric within the spindleand, as a result, it causes vibrations in operation. In certainrotational speed ranges to be passed by the spindle, these vibrationsmay become so strong that they impair the quality of the workpieceprocessing.

On the other hand, if one or more rear guide sleeves for the work barsare dispensed with so as to provide room for a sturdier stock feederinstead, this entails the risk that small diameter work bars will buckleinside the spindle.

It is the object of the invention to remove as far as possible thecauses for such vibrations of the stock feeder and the risk of bucklingof the work bar within the spindle of a guiding device of the kindspecified initially.

This object is met, in accordance with the invention, in that the rearguide sleeve most remote from the chuck has an abutment face remote fromthe chuck for the stock feeder, and that at least this rear guide sleeveis axially displaceable in a direction toward the chuck by means of thestock feeder together with the work bar against the resistance of atleast one spring.

In this manner the stock feeder will hit against the abutment face ofthe rear guide sleeve as the work bar is used up progressively, pushingthe guide sleeve forwardly as the work bar is used up further andadvanced. Thus the spacing between the rear guide sleeve and the chuckis gradually reduced and for this reason the guidance of the rearportion of the work bar becomes ever better and vibrationless. Also thestock feeder is held largely without vibrating by its abutment at therear guide sleeve. Consequently the tendency to vibrate is much reducedas regards the work bar and the stock feeder when comparing them withknown guiding devices of the kind described initially. The above is trueregardless of whether the stock feeder is of telescopic design or hasbut a single axially displaceable rod.

In the case of a preferred embodiment of the invention the or eachdisplaceable guide sleeve is guided in an intermediate tube.

This embodiment is especially well suited for a lathe in which agripping piston is arranged in a cylinder behind the spindle foractuating the collet. In this event the invention conveniently isdeveloped further in that the intermediate tube projects rearwardly outof the spindle and ends in the range of the gripping piston.

Furthermore, it is advantageous if the rear guide sleeve projectstelescopically to the rear out of the intermediate tube when not loadedby the stock feeder.

Finally, it is advantageous if the intermediate tube is exchangeabletogether with all guide sleeves and the associated at least one spring,as a uniform assembly.

Embodiments of the invention will be described further below withreference to diagrammatic drawings in which, in axial sectionalelevation each:

FIG. 1 shows parts of a lathe provided with a guiding and feeding deviceaccording to the invention, shown in a first operational position;

FIG. 2 shows the guiding and feeding device in a second operationalposition;

FIG. 3 shows a modified guiding and feeding device in a firstoperational position; and

FIG. 4 shows the device according to FIG. 3 in a second operationalposition.

FIG. 1 shows a hollow spindle 10 which is part of an automatic lathe. Itis journalled by a plurality of roller bearings 12 in a headstock 14 andnot displaceable axially. The spindle 10 has a front end, at the rightin FIG. 1, at which a front guard ring 18 is removably secured by way ofan intermediate ring 16. A chuck is disposed inside the intermediatering 16 and the front end of the spindle 10.

The chuck comprises a collet 20 supported toward the front on the guardring 18. The collet 20 is formed with an outer conical surface which isenclosed a corresponding inner conical surface of a gripping sleeve 22.The gripping sleeve 22 is guided for axial displacement, at its frontend in the intermediate ring 16 and its rear end directly in the spindle10, and it is loaded by a compression spring 24 acting in the sense ofdisplacement to the rear and being clamped between a rear end face ofthe collet 20 and a corresponding internal shoulder formed in thegripping sleeve 22.

A work bar W extends through the spindle 10, the gripping sleeve 22, andthe collet 20, its front end portion protruding forwardly out of thecollet 20 so as to be worked on. During this work the bar material mustbe clamped as firmly as possible in the collet 20. To this end thegripping sleeve 22 must be loaded by an axially forwardly directed forceconverted into forces which act radially on the work bar W by theconical surfaces of the gripping sleeve 22 and collet 20.

An annular cap 26 engages the rear end of the gripping sleeve 22 and isin threaded engagement with the front end of a gripping tube 28 so as totransmit the axial gripping force. The gripping tube 28 is guided foraxial displacement inside the spindle 10 and in threaded engagement witha gripping piston 30 which operates in an hydraulic cylinder 32. At therear the cylinder 32 is journalled in a stationary bearing box 34, andat the front it is in screw threaded engagement with a flange 36 of atoothed sleeve 38. The toothed sleeve 38 encloses the spindle 10 and isfixed for rotation with the same, a toothed belt (not shown) beingwrapped around the sleeve to drive the same.

An intermediate tube 40 is disposed within the gripping tube 28 so as toproject partly out of the same to the rear, and at its front end it hasa collar 42 which is fastened to the gripping tube 28 by the annular cap26. Locking rings 44 and 46, respectively, are inserted into the frontand rear ends of the intermediate tube 40, the rear locking ring 46delimiting a recess formed in the rear end portion of the intermediatetube 40 and retaining a slip ring 48 which is received in this recess. Aguide sleeve 50 housed within the intermediate tube 40 is supported onthe front locking ring 44.

A rear guide sleeve 52 is likewise received movably in the intermediatetube 40. The rear guide sleeve 52 is shaped like an elongated pipe andcarries a slip ring 54 near its front end and a retaining ring 56 in itscentral portion. A spring 58 is mounted between the two guide sleeves 50and 52 and, as shown in FIG. 1, tends to urge the rear guide sleeve 52to far to the rear that the retaining ring 56 thereof rests against theslip ring 48.

A stop ring 60 is fastened to the rear end of the rear guide sleeve 52and formed at its backside with an abutment or centering face 62 ofhollow conical configuration. The stop ring is guided in a tubularprojection 64 of the gripping piston 30. A stationary oil collector 66is arranged all around the stop ring 60 and formed with a centralaperture 68.

Behind the oil collector 66 a stock feeder 70 is arranged coaxially withthe spindle 10, FIGS. 1 and 2 showing only the front end portionthereof. The stock feeder 70 comprises a tubular feeder casing 72 whichis axially movable but secured against rotation. An outer feeder 76likewise substantially tubular is journalled in the feeder casing 72 byroller bearings 74. A rod-like inner feeder 78 is guided fordisplacement in the outer feeder 76.

FIG. 1 shows the stock feeder 70 in a far advanced position which itadopts when the work bar W, originally several meters long, has beenused up in great part. In this position a conventional bar materialmagazine (not shown) which comprises guide sleeves or roller sets, forexample, can no longer guide and center the work bar W. For this reasona risk of buckling of the work bar W would exist unless it were guidedat a rather small distance from the front end of the stock feeder 70 bythe guide sleeve 50 which extends far to the rear. As the processing ofthe workpiece continues which takes place in front of the collet 20 andthe stock feeder 70 advances the work bar W accordingly, the front endof the outer feeder 76 will pass through the aperture 68 into the oilcollector 66 and hit against the abutment face 62 which has a certaincentering effect on the feeder.

Upon further forward movement the stock feeder 70, acting against theresistance of the spring 58, pushes the rear guide sleeve 52 in forwarddirection until the latter reaches its terminal position shown in FIG.2. The further advancing movement of the work bar W in accordance withthe further workpiece processing is taken care of by the inner feeder 78as it exits progressively from the outer feeder 76, as shown in FIG. 2.At this time the work bar W is continued to be to be guided almostuninterruptedly in the guide sleeves 50 and 52.

If work is to be done on bar material of a different diameter, the guardring 18 is screwed off and the collet 20 together with the grippingsleeve 22 and compression spring 24 are withdrawn from the front end.The annular cap 26 which then is accessible may be loosened from thegripping tube 28 by means of a screw driver. Subsequently theintermediate tube 40 together with its two guide sleeves 50 and 52 andthe spring 58 may be pulled out as an integral assembly from the frontend of the gripping tube 28 or pushed out from the rear. It may then bereplaced by a corresponding assembly including an identical intermediatetube 40 but guide sleeves which are adapted to the new stock diameter.

With the embodiment shown in FIGS. 3 and 4 substantially only partsdisposed inside the intermediate tube 40 differ from those illustratedin FIGS. 1 and 2. As may be taken from FIGS. 3 and 4, the intermediatetube 40 contains a front guide sleeve 80 corresponding in arrangementand essentially also in configuration to guide sleeve 50, and a centralguide sleeve 82, as well as a rear guide sleeve 84, the latter twotogether replacing the guide sleeve 52 and its stop ring 60 according toFIGS. 1 and 2.

The abutment face 62 for the stock feeder 70 is formed at the rear guidesleeve 84 which does not protrude out of the intermediate tube 40 in itsfinal rear position, contrary to the guide sleeve 52. The central guidesleeve 82 rests on the front guide sleeve 80 through intermission of aspring 86, while the rear guide sleeve 84 is supported on the centralguide sleeve 82 by way of a spring 88. The two springs 86 and 88 arecompression springs having the same spring characteristic and mountedunder axial bias.

According to FIGS. 3 and 4 the stock feeder 70 is not divided into outerand inner feeders and has a maximum outer diameter which is smaller thanthe minimum inner diameter of the intermediate tube 40.

When the work bar W becomes shorter than shown in FIG. 3 because itsfront end is being turned off, the stock feeder 70 enters into theintermediate tube 40 and hits against the abutment face 62. From then onthe stock feeder 70 pushes the rear guide sleeve 84 ahead of itself, thetwo springs 86 and 88 which are mutually balanced being compresseduniformly so that the central guide sleeve 82 will move on in a manneras to always maintain a central position between the other two guidesleeves 80 and 84. At this time the work bar W is being guided by allthree guide sleeves 80,82, and 84 until the springs 86 and 88 will havebecome totally compressed. What remains at that point of the work bar Wcan be worked only under the condition that the simple stock feeder 70as shown in FIGS. 3 and 4 is replaced by a stock feeder divided into aninner feeder and an outer feeder in accordance with FIGS. 1 and 2.

What is claimed is:
 1. A guiding and feeding device for a work bar (W) in a lathe, comprising:a hollow work spindle (10) having a front end and a rear end, a chuck (20) attached to the front end of the work spindle (10), an actuating tube (28) guided for axial displacement within the work spindle (10), an actuating piston (30) arranged in a cylinder (32) behind the rear end of the work spindle (10), the actuating tube (28) interconnecting the acuating piston (30) and the chuck (20) so as to transform an axial force generated by the actuating piston (30) into a clamping force exerted by the chuck (20) onto the work bar (W), an intermediate tube (40) disposed within the actuating tube (28) and having a front end near the chuck (20) and a rear end near the actuating piston (30), a front guide sleeve (50 or 80) arranged stationarily within the intermediate tube (40) at the front end thereof and adapted for guiding the work bar (W), a rear guide sleeve (52 or 84) axially spaced from the front guide sleeve (50 or 80), said rear guide sleeve (52 or 84) being adapted to guide the work bar (W) and having a rear abutment face (62), the rear guide sleeve (52 or 84) being guided for axial displacement within the intermediate tube (28) and, in a position of rest, cooperating with an abutment at the rear end of the intermediate tube (28), at least one spring (58 or 88) tending to keep the rear guide sleeve (52 or 84) in its position of rest, and a stock feeder (70) aligned with the work spindle (10) and reciprocable in the axial direction thereof to advance the work bar (W), the stock feeder (70) being adapted to abut against the rear abutment face (62) of the rear guide sleeve (52 or 84) and urge the same towards the front guide sleeve (50 or 80).
 2. The device of claim 1, wherein the rear guide sleeve (52), in its position of rest, projects telescopingly to the rear end out of the intermediate tube (40).
 3. The device of claim 2, wherein the intermediate tube (40) together with all guide sleeves (50, 52; 80, 82, 84) and the associated at least one spring (58; 86, 88) are exchangeable as a constructional unit.
 4. The device of claim 1, wherein a central guide sleeve (82) is arranged between, and axially spaced from, the front and rear guide sleeves (80 and 84, respectively), springs (86, 88) being interposed between the central guide sleeve (82) and each of the front and rear guide sleeves (80, 84).
 5. The device of claim 4, wherein the intermediate tube (40) together with all guide sleeves (50, 52; 80, 82, 84) and the associated at least one spring (58; 86, 88) are exchangeable as a constructional unit.
 6. The device of claim 1, wherein the intermediate tube (40) together with all guide sleeves (50, 52; 80, 82, 84) and the associated at least one spring (58; 86, 88) are exchangeable as a constructional unit.
 7. The device of claim 6, wherein the intermediate tube (40) together with all guide sleeves (50, 52; 80, 82, 84) and the associated at least one spring (58; 86, 88) are exchangeable as a constructional unit. 